This invention relates to a tensioner which provides a fixed tension to a chain or a timing belt which drives a cam shaft of an engine of a car. The tensioner is generally used as a chain or a belt tensioner to an engine. The tensioner operates to push the chain or the belt in a certain direction, directly or indirectly, so as to maintain a fixed tension when the chain or the belt is extended and slackens by friction.
Such a tensioner is adapted to be inserted into a casing by screwing a rotary body and an urged body to energize the rotation of the rotary body with a spring force and change the rotation force of this rotary body to a propelling force of the urged body to advance the urged body from the casing. The top end of the urged body always urges the chain or the like, thereby maintaining a fixed tension.
Further, the top end of this tensioner is covered with an elastic boot and an opening hole is sealed with a seal bolt formed at the base side to form a sealing construction, thereby maintaining a lubricant oil therein.
Further, in the traditional tensioner, an air escaping hole is formed at a suitable location in order to adjust a pressure change due to a change of inner content of the casing caused by the advancement and retraction of the urged body.
However, in the traditional tensioner having the above construction, lubricant oil leakages from an air escaping hole during storage causes a shortage of lubricant oil at the time of the use.
Further, even if during the use of the tensioner, the lubricant oil leakages from the air escaping hole by a breathing phenomenon due to the vibration added to the tensioner, a belt is soiled which can cause slippage between a pulley and the belt and a suitable driving of the belt is not obtained.
Furthermore, the air escaping hole must be provided at a position where it does not contact with the lubricant oil. The traditional tensioner has various problems such as a limitation of bored position and the like.